From my experience, Mongo DB's entire raison d'etre is "laziness".
* Don't worry about a schema.
* Don't worry about persistence or durability.
* Don't worry about reads or writes.
* Don't worry about connectivity.
This is basically the entire philosophy, so it's not surprising at all that users would also not worry about basic security.
Not only that, but authentication is much harder than it needs to be to set up (and is off by default).
Although interestingly, for all the mongo deployments I managed, the first time I saw a cluster publicly exposed without SSL was postgres :)
I'm sure there are publicly exposed MySQLs too
Most of your points are wrong. Maybe only 1- is valid'ish.
Ultimate webscale!
To the extent that any of this was ever true, it hasn’t been true for at least a decade. After the WiredTiger acquisition they really got their engineering shit together. You can argue it was several years too late but it did happen.